1. Field of the Invention
The present invention relates to a light-receiving member sensitive to an electromagnetic wave such as light in a broad sense, which includes ultraviolet rays, visible light, infrared rays, X-ray, .gamma.-ray, etc., and more particularly to a light-receiving member having an important significance in the image-forming fields such as electrophotography, etc.
2. Related Background Art
In the image-forming fields, the following characteristics are required for photoconductive materials that form a light-receiving layer in a light-receiving member:
(1) High sensitivity PA1 (2) High SN ratio [photoelectric current (Ip)/dark current (Id)] PA1 (3) Possession of absorption spectra matched to the spectrum characteristics of irradiating electromagnetic waves PA1 (4) Possession of rapid light response and desired dark resistance PA1 (5) Harmlessness to human bodies when used. PA1 (1) Japanese Patent Application Laid-Open No. 56-83746 proposes a light-receiving member for electrophotography, which comprises an electroconductive substrate and an a-Si photoconductive layer containing a halogen atom as a constituent element, where the localized level density is reduced in the energy gap by adding 1-40 atomic % of a halogen atom to a-Si, thereby compensating for dangling bonds and obtaining suitable electrical and optical characteristics as a photoconductive layer in the light-receiving member for electrophotography. PA1 (2) Japanese Patent Application Laid-Open No. 54-145540 proposes a light-receiving member for electrophotography, where the photoconductive layer is composed of amorphous silicon containing carbon, that is, amorphous silicon carbide, which will be hereinafter referred to as "a-SiC". It is known that a-SiC has high heat resistance and surface hardness, a higher dark resistivity than that of a-Si, and a variable optical band gap in a range of 1.6 to 2.8 eV by the carbon content. The Japanese Patent Application discloses that use of a-Si containing 0.1-30 atomic % of carbon atoms as a photoconductive layer in the light-receiving member for electrophotography, where the carbon atoms are used as a chemically modifying substance, produces distinguished electrophotographic characteristics such as a high dark resistance and a good photosensitivity. PA1 (3) Japanese Patent Publication No. 63-35026 proposes a light-receiving member for electrophotography, which comprises an electroconductive substrate, an intermediate layer of a-Si containing a carbon atom and at least one of hydrogen atoms and fluorine atoms as constituent elements, which will be hereinafter referred to as "a-SiC(H,F)", and an a-Si photoconductive layer, successively laid on the electroconductive substrate, where cracking or peeling of the a-Si photoconductive layer is intentionally reduced by the a-Si intermediate layer containing at least one of hydrogen atoms and fluorine atoms without deteriorating the photoconductive characteristics. PA1 (4) Japanese Patent Application Laid-Open No. 58-219560 proposes a light-receiving member for electrophotography, which comprises a surface layer of amorphous hydrogenated or fluorinated silicon carbide, which will be hereinafter referred to as "a-SiC:H,F", further containing an element belonging to Group IIIA of the Periodic Table. PA1 (5) Japanese Patent Application Laid-Open Nos. 60-67950 and 60-67951 propose a light-receiving member for electrophotography, which comprises a light transmission insulating overcoat layer of a-Si containing carbon atoms, fluorine atoms and oxygen atoms. PA1 (1) When a higher sensitivity and a higher dark resistance are to be obtained at the same time, a residual potential has been often observed in the actual service, and in case of prolonged service accumulation of fatigue due to repeated use has occurred to produce the so called ghost phenomena. PA1 (2) It has been difficult to obtain high levels of chargeability and prevention of smeared images at the same time. PA1 (3) In order to improve the photoconductive characteristics and electrical characteristics such as resistance, etc., hydrogen atoms (H), halogen atoms (X) such as fluorine atoms (F) and chlorine atoms (Cl), or boron atoms (B) or phosphorus atoms (P) for control of electrical conduction type, or other atom species for improving other characteristics have been added to the photoconductive layer as constituent atoms, and there have been problems in the electrical characteristics, photoconductive characteristics or uniformity of the resulting layer, depending on the state of added constituent atoms. That is, when there is an unevenness in the charge transfer ability throughout the photoconductive layer, an uneven image density appears. Particularly in case of halftone image, it is much pronounced, and thus a higher evenness has been required for the layer from the structural, electrical and optical viewpoints. PA1 (4) Temperature of a light-receiving member for electrophotography changes due to the initiation state of an apparatus for heating the light-receiving member for electrophotography to stabilize an electrostatic latent image, fluctuation in the temperature control or change in the room temperature, and consequently the dark resistance changes, resulting in occurrence of uneven image density among the images when copy images are continuously obtained. PA1 (5) Uneven image density has been often pronounced among the images due to fatigue caused by repeated use in the prolonged service. PA1 (6) In the case of obtaining higher chargeabilty and sensitivity at the same time, smeared images have been liable to appear and it has been difficult to maintain image characteristics of high quality without any smeared image in the prolonged service.
Particularly in the case of light-receiving members for electrophotography which are incorporated in electrophotographic apparatuses for office services such as office machines, the harmlessness when used, as mentioned under the item (5), is important. From this viewpoint, amorphous silicon, which will be hereinafter referred to as "a-Si" is regarded as an important photoconductive material, and its application as light-receiving members for electrophotography is disclosed, for example, in DE-A-2746967 and DE-A-2855718.
FIG. 1 is a schematic cross-sectional view of a layer structure of a conventional light-receiving member 200 for electrophotography. The light-receiving member 200 for electrophotography comprises an electroconductive substrate 201 and a light-receiving layer 202 composed of a-Si. The light-receiving layer 202 comprises a photoconductive layer and a surface layer successively laminated on the electroconductive substrate 201 generally by forming these layers on the electroconductive substrate 201 heated to 50.degree.-400.degree. C. by vacuum vapor deposition, sputtering, ion plating, hot CVD, photo CVD, plasma CVD or other film-forming process. Particularly, a plasma CVD process, that is, a process for forming an a-Si deposition film on an electroconductive substrate 201 by decomposing a raw material gas by DC glow discharge, high frequency glow discharge or microwave glow discharge, is suitable and has been practically used so far.
The following light-receiving members for electrophotography have been so far proposed:
The conventional light-receiving members for electrophotography containing a photoconductive layer comprising an a-Si material are improved in the individual characteristics, for example, electrical characteristics such as dark resistance, etc.; optical characteristics such as photosensitivity, etc.; photoconductive characteristics such as light response, etc.; service circumstance characteristics; chronological stability; and durability, but actually still have room for improvements in overall characteristics.
Particularly a higher image quality, a higher speed, and a higher durability are now keenly desired for electrophotographic apparatuses, and as a result further improvements in the electrical characteristics and photoconductive characteristics and also in the durability in any service circumstance are required for the light-receiving members for electrophotography, while maintaining a high chargeability and a high sensitivity.
For example, when an a-Si material is used as a light-receiving member for electrophotography, there have been the following disadvantages:
As a result of recent improvements of the optical light exposure system, the developing system and a transfer system in electrophotographic apparatuses to improve the image characteristics of electrophotographic apparatuses, more improvements have been required also for light-receiving members for electrophotography. Particularly as a result of improvements in the image resolution, reduction of coarse images (unevenness in the fine image density zone) and reduction of spots (black or white spot image defects), particularly 10 reduction of fine spots, which have been so far disregarded, have been keenly desired.
Particularly, spots are due to abnormal growth of a film called "spherical projections", and it is important to reduce the number of the spherical projections. In case of continuous formation of a large number of images, more spots are observable sometimes on the later images than on the initial images as a phenomenon, and thus reduction of increased spots due to the prolonged service has been also desired.
The spots so generated include the so called "leak spots" generated by accumulation of transfer sheet powder on the charging wires of a shared electrostatic charger in case of continuous image formation, thereby inducing an abnormal discharge and bringing a portion of the light-receiving member for electrophotography to a dielectric breakdown. Furthermore, due to the abnormal growth of "spherical projections", etc. on the surface of the light-receiving member for electrophotography, the cleaning blade is damaged after repetitions of continuous image formation, resulting in poor cleaning and deterioration of image quality. Toners are accumulated on the charging wires of a shared electrostatic charger due to scattering of residual toners toward the shared electrostatic charger, and abnormal discharge is liable to be induced. This is also a cause of "leak spot" generation. Furthermore, dropoff of relative large abnormal growth parts due to friction between the light-receiving member for electrophotography and the transfer sheets or the cleaning blade is also a for the spot increase.
Other adverse influences include easy wearing of separator nail for separating the transfer sheets from the light-receiving member for electrophotography due to the abnormal growth and easy occurrence of transfer sheet clogging due to the separation failure.
Use of reprocessed sheets is now increasing even in the electrophotographic apparatuses as a result of the recent policy for protecting the global atmosphere. In case of reprocessed sheets, dusting of additives or paper powder from the paper-making process is more than in the case of conventional fresh paper making. For example, the surfaces of the light-receiving members for electrophotography are damaged by additives used as a bleaching agent for waste newspapers such as China clay, etc., or rosin, etc. used as a size (a surface-treating agent) deposit on the surfaces of the light-receiving members for electrophotography to causing fusion of toners or formation of smeared images. Thus, improvement of reprocessed sheet quality and at the same time further improvement of the surfaces of the light-receiving members for electrophotography have been also desired.
That is, from the viewpoint of reduction of image defects and durability of an image-forming apparatus, prevention of occurrence of abnormal growth as a reason for the image defects, an increase in the durability to a high voltage and a considerable increase in the durability under every circumstances have been required for the light-receiving member for electrophotography, while maintaining the electrical characteristics and photoconductive characteristics at higher levels.
Furthermore, when the photoconductive layer of a light-receiving member for electrophotography is formed at a higher deposition rate by a process for forming a deposition film such as a microwave plasma CVD process, which will be described later, to reduce the production cost of the light-receiving member for electrophotography, the film quality sometimes becomes uneven, or fine cracking or peeling sometimes appears on the a-Si film due to stresses within the film, resulting in yield reduction in the productivity.
Thus, improvements of characteristics of a-Si materials themselves have been attempted, and at the same time overall improvements of layer structure, chemical composition of each layer and processes for forming layers have been desired to solve the foregoing problems.